GB2124680A - Drilling of wells with top drive unit - Google Patents

Description

1 GB 2 124 680 A 1

SPECIFICATION

Drilling of wells with top drive unit This invention relates to well drilling equipment including a top drive assembly having a motor driving a rotary element connected to the drill string to turn it.

A prior top drive drilling rig of this general type includes a pipe handling mechanism consisting of a torque wrench for making and breaking connections and an elevator for suspending a pipe section, both of which are attached to the power driven rotary element of the top drive assembly and rotate with it.

A pipe handler embodying the present invention greatly facilitates the making and breaking of connections and the handling of sections of pipe by utilizing a torque wrench and elevator at least one of which, preferably both, are retained against rotation with the drill string during drilling. Balancing problems and dangerto personnel and equipment which have been encountered in prior equipment as a result of rotation of the torque wrench and elevator during drilling are thus avoided. In addition, these non-rotating parts may be permanently oriented for more convenient access to personnel both at the rig floor and at an elevated location in the rig. Further, all power and control connections to the torque wrench may remain attached to the wrench at all times permitting the wrench to make and break pipe connections at any level in the rig.

In the drawings:

Figure 1 shows a rig embodying the invention; Figure 2 is an enlarged view showing a portion of Figure 1; Figure 3 is a side view on line 3-3 of Figure 2; Figure 4 shows a portion of Figure 2 with the elevator retracted; Figure 5 is a horizontal section on line 5-5 of Figure 2; Figure 6 is a vertical section on line 6-6 of Figure 5; Figures 7, 8 and 9 are horizontal sections on lines 7-7, 8-8 and 9-9 of Figure 3; Figures 10, 11 and 12 are enlarged vertical sec- tions on line 10-10 of Figure 2 showing the apparatus110 in three different conditions; Figures 13A, 138,13C, 13D and 13E represent several steps during addition of a stand of pipe to the drill string; and Figures 14A, 148 and 14C show several steps 115 during removal of a stand of pipe from the drill string.

Rig 10 in Figure 1 includes a mast or derrick 11 projecting upwardly from a rig floor 12, with a tubular drill string 13, formed of a series of pipe sections interconnected at threaded joints 17, extending downwardly along a vertical axis 14 and carrying a bit 15 to drill a well 16. A slip bowl 18 mounted in the rig floor 12 has downwardly tapering surfaces engageable with tapering surfaces of wedge slips 19 to support the drill string while a section of pipe is added to or removed from the string. The string is rotated during drilling by a top drive drilling assembly 20 suspended by a hook 26 of a hoisting mechanism 21 which includes a traveling block 22 movable vertically relative to a crown block 23 by a line 24 pulled by draw works 25. Assembly 20 carries at its underside a pipe handling mechanism 27 embodying the invention for making and break- ing threaded connections in the drill string and for moving sections of drill pipe between active and inactive positions.

The top drive assembly, pipe handler and associated parts are mounted for movement along vertical axis 14 by two spaced parallel vertical tracks 28 which extend parallel to axis 14 and are preferably of Pshaped horizontal section, and may extend downwardly from the top of the derrick to lower extremities 29 above the rig floor. Assembly 20 may include a conventional swivel 31 connected to the upper end of a power unit 30 and suspended by a bail 32 from hook 26 hanging from traveling block 22. Circulating fluid flows into the swivel through a gooseneck 33 and downwardly through the tubular stem 34 of the swivel which is mounted by bearings 36 and for rotation relative to the non-rotating swivel body 35 and is supported from the body by those bearings. Power unit 30 includes a carriage 37 guided by tracks 28 for movement vertically along axis 14 and including two vertical structures 38 of U-shaped horizontal section disposed partially about the tracks 28 and carrying rollers 39 at the upper and lower ends of structure 38 for engaging the tracks (Figure 5) to roll therealong and prevent movement of the carriage 37 in any direction except vertically. Members 38 are rigidly interconnected by members 40.

Power unit 30 includes a housing 41 which during drilling is fixed rigidly to the carriage, and a short tubular sub 42 journalled by bearings 43 for rotation relative to housing 41 about axis 14. These bearings function also as thrust bearings retaining housing 41 against vertical movement relative to sub 42 and supporting the housing and a contained motor 44 from the sub. The motor may be electrically ener- gized and drive sub 42 rotatively through reduction gears and about axis 14 relative to housing 41 in either direction, under the control of an operator through a remote control console 45 connected to the motor by a line 245 and flexible service loop 46 containing electrical cables and hydraulic lines leading to the vertically movable power unit. The end 246 of loop 46 may be connected to the derrick vertically midway between the rig floor and the top of the derrick to provide electrical and hydraulic connections to the power unit in all positions thereof. Housing 41 may be attached rigidly to a framework 47, which is connected to carriage 37 for swinging movement about a vertical axis 52 between the full line and broken line positions of Figure 5 by a pivot pin 48 on the carriage projecting upwardly into a bearing 49 in the bottom of framework 47, and an aligned second pivot pin 50 projecting upwardly from the framework into and rotatably received within a bushing 51 carried by the carriage. Frame- work 47 may be releasably retained in the active full line position of Figure 5 by bolts 53 mounted to the carriage to pivot about a vertical axis 54 between the Figure 5 locking position of reception within a recess 253 in a member 55 carried by framework 47 and a laterally swung released position, with a nut 56 2 GB 2 124 680 A 2 being tightenable on the bolt against member 55 to releasably lockthe framework and carried parts in their Figure 5 position. The upper end of sub 42 of power unit 30 is threadedly connected to the rotary stem 34 of swivel 31, to pass fluid from the swivel through sub 42 to the drill string.

Pipe handling mechanism 27 includes a tubular sub 57 threadedly connected at 58 to and driven by sub 42 and having external threads 59 connectible to the drill string 13 to drive it, with the drilling fluid flowing through an internal passage 60 to the string. Sub 57 may include an upper main section 61 and a lower relatively short replaceable section 62 connected to section 61 by threads 63 which are desirably larger in diameter than threads 59 and the threads of other joints in the drill string, and are made up to a torque much higher than that at which threads 59 are connected to the drill string and the other joints in the string are made up, so that during normal handling the connections at threads 59 and between an upper section of the drill pipe and the remainder of the drill string can be broken without detaching the parts at 63. Sections 62 and 61 have outer cylindrical surfaces 64 and 65 of a common diameter with an annular upwardly facing inclined shoulder 66 formed on a cylindrical flange 67 on section 61. Therebeneath, section 61 has a circular series of parallel axial splines 68.

A hanger assembly 70 suspends from housing 41 a torque wrench 69, including an upper section 71 containing a circular series of axial parallel splines 72 movable vertically into and out of interfitting engagement with splines 68 of sub 57, and a lower section 73 disposed about and adapted to releasably grip the upper joint end of a top section of drill string 13. Section 73 of the torque wrench includes a rigid body structure formed of two sections 74 and 75 detachably interconnected by pins 76 and 77 and forming together a passage 78 receiving the drill pipe, a jaw 79 carrying gripping elements 80 engageable with the upper end of a section of drill pipe, and a second jaw 81 having gripping elements 82 engaging the opposite side of the pipe. A piston 83 is actuable within a cylinder chamber 85 in section 75 toward and away from axis 14 and is connected to jaw 81 by screws 86 to hydraulically move jaw 81 toward and away from jaw 79 to grip and release the pipe. Elements 80 and 82 have teeth capable of applying torque to the gripped pipe. Section 73 is turned about axis 14 relative to section 71 by piston 115 and cylinder mechanisms 87, whose cylinders 88 are connected to bodypart 75 by trunnions 89 for slight relative pivotal movement about vertical axes 90, and whose pistons have their rods 91 connected by pins 92 to ears 93 on body member 71 for relative pivotal movement. A guard 95 may project right wardly from body 75. Two tapering bell segments 96 projecting downwardly from body 74 of the torque wrench form a downwardly flaring internal throat for centering the upper end of a drill pipe section as it and the wrench are moved axially relative to one another. Hydraulic fluid is supplied to cylinders 85 and 88 through service loop 46 to allow the torque wrench to be actuated into and out of gripping engagement with the well pipe by actuation of 130 6 control elements at the remote console 45, and to allow pressure fluid to be supplied to cylinders 88 selectively for turning the section 73 of the torque wrench about axis 14 relative to upper section 71 in either direction to make or break the connection at 63.

When the gripping elements of the torque wrench are released, and the drill string is being driven rotatively, the torque wrench may be centered by two replaceable wear parts 97 and 98 which are carried at the top of body part 74 and have inner curved surfaces 99 engageable with the top section of the rotating drill string to prevent its contact with any other portion of the wrench and thus avoid wear of any parts other than elements 97 and 98. Part 98 may be movably secured to jaw 81 by two bolts 100 extending vertically through the jaw and through slots 101 in part 98 in a manner enabling jaw 81 in its active pipe gripping position (Figure 11) to project beyond edge 99 of part 98 and engage the pipe. When jaw 81 is retracted rightwardly (Figure 10), engagement of portions 102 of part 98 with two shoulders 202 on body part 75 limits rightward movement of part 98 while piston 83 and jaw 81 continue to move far enough to retract gripping elements 82 rightwardly beyond edge 99 of part 98 (Figure 10), so that edge 99 may locate the rotating pipe string while protectig gripping elements 82 from contact therewith, Part 97 is attached to jaw 79 by two screws 200 extending vertically through the jaw and through slots 201 formed in part 97 and permitting movement of part 97 leftwardly and rightwardly relative to the jaw. Springs 203 bear in opposite directions against part 97 and shoulders 204 on body part 74 to urge part 97 rightwardly relative to part 74 and jaw 79 toward the Figure 10 position to center the pipe during drilling, but with part 97 being actuable to the retracted position of Figure 11 leftwardly beyond gripping elements 80 when the pipe is gripped by elements 80 and 82 of the torque wrench. The bolts 100 and 200 may also secure bell sections 96 movably to jaws 79 and 81 by extension through slots 101 and 102 in flange portions 97a and 98a of sections 96, to allow movement of parts 97a and 98a and their bell portions 96 in the same manner as parts 97 and 98, with part 97 being urged rightwardly by springs corresponding to springs 203 associated with part 97.

The torque wrench hanger 70 includes a rigid vertically extending member 103 having a bifurcated upper connecter portion 104 attached by a pin 105 to a cylindrical portion 106 of housing 41. Pin 105 extends through apertures in structures 104 and 106 and retained against detachment from the other parts by a screw 108 extending through a tab 107 on the pin. The lower end of member 103 is connected to the piston 109 of a piston and cylinder mechanism 110 whose cylinder 111 has its lower end rigidly connected to member 75 of the torque wrench. Rod 112 of piston 109 is threaded connected at 113 to a screw 114 whose upper large diameter end is threadedly connected at 115 to a part 116 attached to member 103. Admission of pressurized hydraulic fluid to the upper end of cylinder 111 forces the 1 1% 4V 3 GB 2 124 680 A 3 cylinder upwardly to bring splines 72 on part 71 into interfitting engagement with splines 68 on sub 57 and prevent rotation of sub 57 relative to part 71. A tube 117 about rod 112 limits upward movement of the torque wrench, by engagement at its opposite ends with cylinder 111 and a flange 214 on part 114, in the Figure 11 position in which the splines interfit only partially. In that position, gripping elements 80 and 82 of the lower section 73 of the torque wrench engage and grip the top section of the drill pipe. If tube 117 is removed (Figure 12), mechanism 110 can move the torque wrench upwardly far enough to cause splines 68 and 72 to fully interfit and position the gripping elements of the lower torque wrench section 73 to engage section 62, so that the torque wrench can make or break the connection 63 between sections 61 and 62.

A conventional elevator 118 beneath the torque wrench is suspended from a carrier part 119 above the torque wrench by two links 120, and may include two halves 121 and 122 hinged by a pin 123 for relative pivotal movement about the vertical axis of the pin between a closed position encircling a drill pipe section and an open position in which the elevator can be moved laterally onto and off of the drill pipe. A latch mechanism 124 releasably retains the two halves closed. Sections 121 and 122 have complementary semi-circular shoulders forming together an essentially annular composite upwardly facing shoulder 125 when the elevator is closed, which shoulder flares upwardly in correspondence with an annular undersurface 126 of a joint end of the drill pipe, to suspend the drill pipe from the elevator. Loops 127 on the elevator halves are connected at diametrically opposite locations to loops 128 of links 120, with removable closure elements 129 extending across the outer sides of loops 127 to maintain the connection. Loops 130 at the upper ends of the links connect to loops 131 on carrier part 119 closed by removable straps 132.

Parts 119 and 118 are guided for vertical movement between the positions of Figures 2 and 4, and restrained against rotary movement, by two torque arresting assemblies 133 extending vertically along parallel vertical axes 134 at opposite sides of axis 14.110 Each assembly 133 includes a vertical cylinder 135 centered about one of the axes 134 and slidably received within one of two vertical cylindrical passages 136 in part 119. Annular flanges 137 on cylinders 135 limit downward movement of part 119 115 in the Figure 2 position. A piston 138 movable vertically in each cylinder has an upwardly projecting rod 139 with a bifurcated portion 140 attached by a pin 141 to ring portion 106 of housing 41. Sub 57 extends vertically through a central passage 142 in part 119, having a lower cylindrical portion 143 within which enlargement 67 on the sub is movably received and confined, and having a reduced diameter upper circular portion 144 within which the upper externally cylindrical reduced diameter portion 65 of the top section of the sub is received. An annular bushing 145 carried by part 119 closely engages the sub to journal itfor rotation and assist in guiding part 119 forvertical movement. A down- wardlyfacing annular inclined shoulder 146 in part 119 is engageable with the correspondingly inclined shoulder 66 on the sub to support part 119 and the suspended elevator from sub 57 when the entire weight of the drill string is supported bythe elevator.

At other times, as when only a stand of drill pipe detached from the string is supported by the elevator, shoulder 146 is maintained above shoulder 66 by a series of Belleville washers 147 disposed about the piston rods 139 above pistons 138 with in cylinders 135yieldingly urging the cylinders upwardly relative to the pistons to the Figure 11 position. Part 119 and the elevator and drill pipe section are then suspended from the housing of power unit 30 Vieldingly through assemblies 133. When the drilling assembly moves downwardly to a location near the rig floor, the elevator and torque wrench move progressively closer together axially, so that both can move as close to the level of the rig floor as possible (see Figure 4). This maximizes the range of vertical movement of the drilling apparatus, and also enables detachment of the drilling unit from the drill string close enough to the rig floor and slips 19 to avoid distortion of the string while making or breaking a connection. To automatically move the elevator and torque wrench relatively toward one another, the apparatus includes a flexible cable 148 having parts 149 at its ends with eyes 150 attachable by bolts to carrier 119 at diametrically opposite locations. From one of the elements 149, the cable extends upwardly at 152, then about a sheave 153 which is mounted to housing 41 for rotation about a horizontal axis 154, then horizontally at 155 and about a sheave 156 mounted to frame 47 for rotation about a normally vertical axis 157, then horizontally at 158, then about a sheave 159 mounted to frame 47 for rotation about a normally vertical axis 160, then about a sheave 161 mounted to housing 41 for rotation about a horizontal axis 162, and finally downwardly at 163 to the second element 149.

When the drilling motor is moved downwardly beyond the position of Figure 1, portion 158 of cable 148 engages a stationary part 164which may be midway between the two tracks 28, and attached to an element 167 projecting from a rigid member 165 connected at its ends to members 166welded to the tracks. The central portion of the cable is received within a semicircular groove 168 in part 164, and is retained thereby against downward movement as the motor and the other parts continue their downward movement, causing the cable ends 152 and 163 to be pulled upwardly toward sheaves 153 and 161, and thus retract part 119 upwardly toward housing 41 to the Figure 4 position, or stated differently acting to half downward advancement of part 19 and the elevator while the torque wrench and connected parts continue their downward advancement to positions near the elevator. Sheaves 156 and 159 may be mounted to pivot bodily about parallel horizontal axes 169 to properly engage the cable as the portions thereof between part 164 and sheaves 156 and 159 change f rom horizontal condition to more vertically extending condition. During a drilling operation, while drilling fluid is pumped downwardly through motor driven stem 42, sub 57 and the drill string, thse elements are driven rotatively by motor 4 GB 2 124 680 A 4 44 to drill the well. This apparatus is all suspended from the derrick by traveling block 22 and line 24, with draw works 25 paying out the line to lower the top drive assembly and string as the bit advances.

The elevator is suspended in the relative position of Figures 2 and 3 until it nears the rig floor, at which time cable 148 contacts part 164 and holds the elevator in essentially that position while the other parts continue their downward movement to the Figure 4 condition. The driller then sets the slips 19 on the upper portion of the upper section of the string, to suspend the string by the slips.

The circulation of drilling fluid is halted, and sub 57 is detached from the string by actuating controls at console 45 to first apply pressure fluid to piston and cylinder mechanism 110 in a manner raising the torque wrench 69 to the position of Figure 11, bringing splines 72 and 68 into interfitting engagement, and then supplying presssure fluid to cylinder chamber 85 causing the lower section of the torque wrench to grip the top section of the drill string. Pressure fluid is then supplied to piston and cylinder mechanism 87 to turn section 71 of the torque wrench relative to its lower section 73, forcibly unscrewing the string and sub 57 from their tightly engaged condition. After the threaded connection has thus been broken, the pressure f luid to the various portions of the torque wrench and its elevating piston and cylinder mechanism 110 is released to lower the torque wrench out of engagement with splined 68 and release the gripping engagement of the lower section of the torque wrench with the top section of the pipe string. Motor 44 is then energized to spin sub 57 rapidly in a direction unscrewing that sub from the string. With the elevator open, the top drive drilling assembly is then raised by the draw works and hoisting mechanism from the position of Figure 13A through the full line position of Figure 13B to the elevated broken line position of that Figure above the upper end 160 of a stand of l5ipe 13a in a rack 161 in the side of the derrick. The elevator is then swung over to a positon about the upper portion of stand 13a just beneath its enlarged upper joint end, and is closed about the stand, after which the draw works are actuated to pull the elevator and related parts upwardly lifting the stand 13a by the elevator and allowing itto swing to a positon directly above the upper end of the drill string. The apparatus is then lowered to stab the bottom end of the suspended stand into the upper end of the string at floor level (Figure 13C), after which the top drive drilling assembly and pipe handling mechanism are lowered as represented in Figure 13D until sub 57 has its threads 59 received within the upper box end of stand 13a. Motor 44 is energized to rotate sub 57 rapidly, spinning it into the upper end of sand 13a and then spinning the lower box end of stand 13a into the drill string, with this rotation developing sufficient torque to make up the connections at both ends of stand 13a to a properly torqued condition. The top drive assembly is then raised slightly to allow removal of slips 19, freeing the string for powered rotation by the top drive unit to continue drilling.

A stand is removed by a reverse process (Figures 130 14A-14C). The top drive apparatus may first be elevated by the traveling block while maintaining circulation and rotation to ream out of the hole. When the apparatus reaches the Figure 14A positon, in which the lower end of the stand to be removed is just above floor level, slips 19 are set to suspend the string just below that stand, after which that stand is broken out from the string by tongs or other equipment and then spun out. The connection between the stand to be removed and sub 57 is then broken utilizing torque wrench 69, by first elevating the wrench as discussed and then actuating it to grip the upper end of the stand to be removed and then relatively rotate sections 71 and 73 of the torque wrench to apply torque in a direction unscrewing sub 57 from the stand. The sub 57 is then spun out from the stand by rapidly rotating it utilizing motor 44. Elevator 118 is closed about the stand beneath its upper enlarged joint end, and sub 57 is then spun out from the stand by energizing the motor to rapidly rotate the sub, leaving the stand suspended by the elevator (Figure 14B). The draw works are actuated to raise the top drive drilling equipment causing the elevator to hoist the free stand from the drill string, with the stand then being swung to the Figure 14C position for storage in the rack. The elevator is unlatched and removed from the stand, and the apparatus is then lowered to stab the sub 57 into the next section of the drill string, with the sub being spun into that section by motor 44 with enough torque for elevation of the string high enough to remove the next successive stand, etc.

If it is desired to remove section 62 of sub 57 from the upper section 61, to allow replacement of section 62 if its threads 29 become worn, stop sleeve 117 is removed from its normal positon about piston rod 112. To enable such removal, the sleeve may be slotted along its axis and retained by bolts to cylinder 110. With tube 117 removed, the piston and cylinder mechanism 110 can be actuated to pull the torque wrench upwardlyto the Figure 12 position, in which splines 72 arefully engaged with splines 68. The gripping elements of jaws 79 and 100 are then forced against section 62 of sub 57 by piston 83, to grip and hold section 62 against rotation while part 71 is turned by piston and cylinder mechanism 87 to rotate section 61 relative to section 62 in an unscrewing direction for removal of section 62 from section 61. The parts can be reconnected by reverse actua- l 15 tion of the parts.

Claims (12)

1. Apparatus for use with atop drive assembly which includes an element to be connected to and turn the upper end of a drill string and motor means for turning said element, said apparatus comprising a powered torque wrench at the lower end of said assembly for applying torque in opposite directions to said string and element, an elevator at the lower end of said assembly for engaging and suspending a section of said drill string beneath the torque wrench, and connecting means attaching said torque wrench and elevator to the top drive assembly for movement upwardly and downwardly therewith I- GB 2 124 680 A 5 and, suspending the elevator and a section of the drill string from the top drive assembly, characte rized by said connecting means retaining at least one of said torque wrench and said elevator against rotation with said element and the drill string as said element and string are rotated by said motor means to drill a well.

2. Apparatus as claimed in claim 1, in which said connecting means retain both the torque wrench and elevator against powered rotation with said element and drill string.

3. Apparatus as claimed in either of the preced ing claims, in which said torque wrench and said element have portions relatively movable between active positions interfitting to prevent relative rota tion between a section of the torque wrench and said element and inactive positions freeing said element for powered rotation relative to the torque wrench during drilling.

4. Apparatus as claimed in either claim 1, or 85 claim 2, in which said element has a splined portion, and said torque wrench has a first section with a splined portion, a second section for gripping the drill string, and powered means for turning said sections relative to one another, said connecting means including a power unit for actuating said torque wrench upwardly and downwardly between an active position in which said splined portions are in interfitting engagement and an inactive position moving said splined portions out of engagementto permit rotation of said element relative to the torque wrench during drilling of a well.

5. Apparatus as claimed in any of the preceding claims, in which said connecting means can suspend the elevator from said element when the element is not rotating but permit rotation of said element and a connected string relative to the elevator during drilling of a well.

6. Apparatus as claimed in any of the preceding claims, in which the torque wrench and elevator are movable closer vertically together in lower positions thereof.

7. Apparatus as claimed in any of the preceding claims, in which said connecting means include a carrier part suspending said elevator and retained againt rotation and movable upwardly and down wardly with the elevator relative to the torque wrench and top drive assembly between a lower position in which the carrier part and elevator are suspended by said element, a higher second posi tion in which said element is rotatable relative to the carrier part and elevator, and a still higher third position.

8. Apparatus as claimed in claim 7, in which said connecting means include torque arrester structures projecting downwardly from a non-rotating section of the top drive assembly and guiding the carrier part for upward and downward movement and yieldingly urging the carrier part upwardly to said second position.

9. Apparatus for use with atop drive assembly which includes an element to be connected to and turn the upper end of a drill string and motor means for turning said element, said apparatus comprising a powered torque wrench at the lower end of said assembly for applying torque in opposite directions to said string and element, an elevator at the lower end of said assembly for engaging and suspending a section of said drill string beneath the torque wrench, and connecting means attaching said torque wrench and elevator to the top drive assembly for movement upwardly and downwardly therewith and suspending the elevator and a section of the drill string from the top drive assembly, characterized by said torque wrench and elevator being relatively movable closer vertically together in lower positions thereof.

10. Apparatus as claimed in claim 9, including means automatically responsive to movement of said top drive drilling assembly and torque wrench to a predetermined lower position to retract said elevator upwardly relative to and toward the torque wrench.

11. Apparatus for use with atop drive assembly which includes an element to be connected to and turn the upper end of a drill string and motor means for turning said element, said apparatus comprising a powered torque wrench at the lower end of said assembly for applyin torque in opposite directions to said string and element, an elevator at the lower end of said assembly for engaging and suspending a section of said drill string beneath the torque wrench, and connecting means attaching said torque wrench and elevator to the top drive assembly for movement upwardly and downwardly therewith and suspending the elvator and a section of the drill string from the top drive assembly, characterized by said connecting means including means for actuating said torque wrench upwardly and downwardly relative to said element between an active position in which portions of said torque wrench and said element interfit to retain said element against rotation relative to said portion of the torque wrench and a released position permitting such rotation.

12. Apparatus as claimed in any of the preceding claims, including said top drive assembly as an element of the claimed combination.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company limited, Croydon, Surrey, 1984. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.